1. Field of the Invention
The present invention relates to an MPEG II (Motion Picture Expert Group II) system, and more particularly, to an MPEG II system with a PES decoder, in which a software basis program stream and a hardware basis transport stream are demultiplexed irrespective of forms of the streams for restoring a video signal and an audio signal.
2. Description of the Related Art
Recently, different formats are suggested for transferring digitized video and audio signals between media. An MPEG II decoder formats a video compressed data and an audio compressed data for easy transfer of the data between media. There are formats provided for transmission/reception under an ambient in which almost no transmission error occurs, such as storage media, and formats provided form transmission/reception under an ambient in which transmission errors are liable to occur, such as satellite or cable. The format for a transmission/reception devices for the ambient in which almost no transmission error occurs is formed with program streams (hereafter called as "PS"), and the format for a transmission/reception devices for the ambient in which transmission errors are liable to occur is formed with transport streams (hereafter called as "TS"). That is, the PS and the TS has a difference in use of an error correcting code system. In the MPEG II decoder, transport scale data are multiplexed into packets containing audio, video, program specific information and other digital data according to respective preset ratios before transmission.
A background art MPEG II decoder in transmission/reception devices for use in an ambient with possible errors employs either a CPU or a hardwired logic. FIG. 1(a)-(e) illustrate a structure of data produced from a compressed data provided through a video encoder at a transmission side through a PES (Packetized Elementary Stream) packetizing, a PS packetizing, a TS packetizing, and FIG. 2 illustrates a background art MPEG II system at a reception side.
Referring to FIG. 1(a), data after the packetizing in the MPEG II decoder has a structure of an access unit in a form of compressed original video signal provided through an encoder. The access unit is added of information on video (aspect ratio, bit rate and etc.) together with a sequence header, to provide an elementary stream as shown in FIG. 1(b), which is processed through the PES packetizing, to provide a PES header and an appropriate length of the elementary stream. Next, the PES packetized data as shown in FIG. 1c is packetized into a TS having packets each with 188 bytes as shown in FIG. 1d if it is intended to be used in an ambient with error. And, if it is intended to be used in an ambient without error, the PES packetized data as shown in FIG. 1c is packetized into a PS having packs each with one or more PES packets as shown in FIG. 1e.
Referring to FIG. 2, the receiver side MPEG II system is provided with a first switching part 1 for selecting a PS data in a storage medium under an ambient of no error in response to a selecting control signal, a second switching part 2 for selecting a TS data under an ambient with errors, a PS demultiplexer 3 for receiving the PS data from the first switching part 1 and demultiplexing pack headers and system headers, a video packet parsing part 4 for receiving and parsing a PES packet data having pack headers and system headers demultiplexed in the PS demultiplexer 3 and providing an elementary stream to a video decoder 5, the video decoder 5 for receiving the elementary stream from the video packet parsing part 4 and decoding a video signal in response to a video control signal, a TS demultiplexer 6 for receiving the TS data from the second switching part 2 and demultiplexing a transport header, an ADF (Adaptation Field), and a PSI (Program Specify Identifier), an audio packet parsing part 7 for receiving and parsing the PES packet data having the transport header, the ADF and the PSI demultiplexed in the TS demultiplexer 6 and providing to an audio decoder 8, and the audio decoder 8 for receiving and decoding an audio signal received from the audio packet parsing part 7 in response to an audio control signal.
The operation of the aforementioned receiver side MPEG II system will be explained with reference to FIGS. 1 and 2.
In the transmitter side, a video signal is encoded into an access unit, a compressed form of an original signal, through an encoder (see FIG. 1a). The access unit data is added of video related information, together with a sequence header, to provide an elementary stream form of data (see FIG. 1b). Then, the elementary stream is passed through a PES packetizing process (see FIG. 1c), to be provided as a PES packet of an appropriate length in a form of PES header and elementary stream(GOP). Next, depending on an application, the PES packetized data (see FIG. 1c) is either provided as a TS (see FIG. 1d) packetized as transport packets each with 188 bytes for use in ambient with errors, or provided as a PS formed with packs each with one or more PES packets for use in an ambient without error. In this instance, since the PS, data of a storage media under an ambient without error, and the TS, data under an ambient with error, are received continuously, a form of data to be provided finally from the continuously received PS and TS is selected by a user or a controller. Therefore, when the first switching part 1 is turned on in response to a selecting control signal, the PS as shown in FIG. 1(e) is selected and provided to the PS demultiplexer 3. The PS demultiplexer 3 demultiplexes pack headers and system headers in the received PS data and provides the demultiplexed video and audio PES packet data to the video packet parsing part 4 and the audio packet parsing part 7. Then, the video packet parsing part 4 and the audio packet parsing part 7 parse the received PS into video or audio data such as PES headers and provide original elementary streams to the video decoder 5 and the audio decoder 8, respectively. In this instance, the video packet parsing part 4 and the audio packet parsing part 7 parse into PS MAP and PS directory and exchange related data with a host computer (not shown) for detecting an overall system structure of the PES packet. And, when the second switching part 2 is turned on in response to a selecting control signal, the TS as shown in FIG. 1(d) is selected and provided to the TS demultiplexer 6. The TS demultiplexer 6 demultiplexes the received TS data into transport headers, ADF and PSI and provides the demultiplexed video and audio PES packet data to the video packet parsing part 4 and the audio packet parsing part 7. Then, the video packet parsing part 4 and the audio packet parsing part 7 parse the received TS into video or audio data such as PSI and only provide original elementary streams to the video decoder 5 and the audio decoder 8, respectively.
However, each of the PS and TS has a stream of information additional to a program. Therefore, the PS data is further required a process for decoding the PES packets each having PS MAP and PS directory at a PES packet decoder, and the TS data is required a process for decoding the TS additional information presenting in the PSI (Program Specific Information) stream, without fail. Therefore, the background art MPEG II system, which requires a separate decoder for the decoding process, has a limitation for application to current multimedia system which requires a variety of functions, causing problems that a complicated decoding process is required and cost of the MPEG II system becomes expensive due to the additional decoder.